Gas filled crosslaminate and method for its manufacture

ABSTRACT

Crosslaminates of thermoplastic films have at least one of the films formed as a fluted structure, and two films are laminated to one another in such a manner that pockets are formed which contain gas. The pockets allow passage of gas between at least two adjacent flutes, whereby the product has an improved handle, and bags formed of the laminate have good stacking properties when filled with coarse particulates. The flute pitch is generally no more than 3 mm, while the pocket length is less than 50 mm. The bonding method involves spot bonding between the films, achieved by adhering the films together between crown portions of bosses on one film with molten material on the other film under a low pressure process, for instance achieved by provision of air pressure through adaptation of production apparatus, for instance die portions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 14/844,848, filedSep. 3, 2015, which is a divisional of U.S. Ser. No. 13/382,809, filedMar. 1, 2012, now U.S. Pat. No. 9,132,602, issued Sep. 15, 2015, whichis a 35 U.S.C. §371 National Phase Application of and claims the benefitand priority to PCT/EP2010/059571, filed Jul. 7, 2010, published asWO2011/003952 on Jan. 13, 2001, which claims the benefit of and priorityto GB 0911822.5, filed Jul. 8, 2009.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The main purpose of the present invention is to provide crosslaminatesof low gauge with an improved feel of substance.

2. Description of the Related Art

A crosslaminate comprising a film (A) which has a waved shape and a film(B) which has a flat shape is known from WO02/102592 Rasmussen, and acrosslaminate comprising two films (A) and (B) which both have wavedshape, with the directions of the two sets of waves crossing each other,is known from WO04/054793 Rasmussen. The general technology ofcrosslaminates, the purposes of the waving (fluting) and methods andapparatus to achieve this structure are explained in these twopublications.

SUMMARY OF THE INVENTION

One purpose of the fluted shape is to obtain improved stiffness inrespect of bending, and another purpose is to give the crosslaminate animproved feel of substance. A further purpose is to improve the heatseal properties. It has also been found that the fluted shape improvesthe tear propagation resistance.

With the increased request for raw material saving there is anincreasing need to reduce the weight per square meter of such flutedcrosslaminates and crosslaminates of related structures, while stillobtaining good stiffness with respect to bending and a clearly improvedfeel of substance, compared to the stiffness and feel of flatcrosslaminates. These goals are objectives of the present invention, andin a first aspect of the invention are achieved by a suitable encasementof gas (normally atmospheric air) between the laminated films.

It is known from the above mentioned WO02/102592, claims 17 and 25, thatthe flutes can be flattened at intervals and bonded across each onesentire width to form a row of narrow closed elongated pockets. Theencased gas (e.g. atmospheric air) helps to provide the laminate withincreased feel of substance and increased stiffness in one direction.

In trials preceding the present inventions the inventors have repeatedthe fluting/crosslaminating procedure described in the example inWO02/102592, however with a much lower gauge of each of the two films inthe crosslaminate, namely 20 g m⁻² referring to the non-fluted shape.The result was a very “sloppy” laminate. Then the flutes were flattenedand bonded at intervals by means of a simple pair of sealer bars heatedto 105° C., so as to encase the air in each of the flutes. Thisconsiderably increased the feel of “substance” and the stiffness in onedirection.

However, this encasement of air also proved to cause problems, e.g.attempts to carry out flexographic printing on the crosslaminate gave apoor result. Furthermore, measurements of friction between two sheets ofthe crosslaminate turned perpendicular to each other (like stacked bags)showed very low values, for the coefficient of friction.

The basic idea behind a first aspect of the present invention is thatthe gas (air) should not be encased in a “one dimensional” pocket namelya pocket which comprises only one flute, but should be encased in a “twodimensional” pocket comprising several flutes, in such a way that withineach pocket there is a passage for gas from each flute to one or both ofthe adjacent flutes.

To try this, the bonding between the waved film (A) and the flat film(B) was not formed as a line bonding as in the known procedure, but wasmade a spot-bonding, and the encasement of gas was not by transversewelding lines alone, but by a combination of transverse and longitudinalwelding lines. In this manner, the gas could freely move from flute toflute within each of the pockets formed by the two systems of weldinglines.

This very considerably improved the printing quality, since the gas wasremoved from the locations which came under pressure. When the printingpressure was released, the gas returned and reshaped the flute. It wasalso found that the handle of the product was improved.

Furthermore it is believed that bags made from such film will showbetter stacking properties, e.g. when the content consists of coarsegrains. This effect will be similar to the mentioned effect of printing.

In accordance with these remarkable results, the first aspect of thepresent invention 1, describes a crosslaminate comprising at least twobonded-together films (A) and (B), each comprising an orientable,crystalline thermoplastic polymer material and each being uniaxiallyoriented or being biaxially oriented with one direction dominating, thedirections in (A) and (B) crossing each other, the bonding being anintermittent bonding which leaves more than 50% of the film areaunbonded and which forms pockets to encapsulate gas, whereby the gaswithin each pocket has a volume which referring to the relaxed state ofthe laminate and 1 atmosphere ambient pressure is at least double thevolume of the polymer material, where a) the gauge of each of the films(A) and (B) is at the highest 30 g m⁻² in the form it has in thecrosslaminate, b) the bonding consists in a combination of a pattern ofrectilinear or curved bonding lines (4), which are combined to form thegas encapsulating pockets, and within each pocket at least 5 spot bonds(3), and c) the longest extension of each pocket in any direction is atthe highest 50 mm. In accordance with these remarkable results, thefirst aspect of the present invention also describes a method ofmanufacturing a crosslaminate comprising at least two bonded-togetherfilms (A) and (B), each comprising an orientable, crystallinethermoplastic polymer material in which each is supplied with uniaxialorientation or being biaxially oriented with one direction dominating,and the directions in films (A) and (B) is brought to cross each other,bonding being carried out as an intermittent bonding which leaves morethan 50% of the film area unbonded and which forms pockets toencapsulate gas, whereby the gas within each pocket has a volume whichreferring to the relaxed state of the laminate and 1 atmosphere ambientpressure at least is double the volume of the polymer material, where a)the gauges of starting materials and conditions of orientation are suchthat the gauge of each of the films (A) and (B) is at the highest 30 gm⁻² in the form it has in the crosslaminate, b) the bonding is carriedout as a combination of a patterns of rectilinear or curved bondinglines (4), which are combined to form the gas encapsulating pockets, andwithin each pocket at least 5 spot bonds (3) and such that c) thelongest extension of each pocket in any direction is at the highest 50mm.

In this connection the volume of the gas in a certain pocket can bedetermined by cutting out the pocket and measuring its buoyancy in wateroptionally containing a low level of surfactant to minimize air bubbleattachment at the product surface, while the corresponding volume of thepolymer material is determined by the weight of the pocket divided bythe density of the polymer material.

In this structure one film (A) and optionally also the second film (B)may have a fluted shape, where the film (A) has a fluted shape, thepitch of the flutes (103) measured from middle to middle of adjacentflutes on the same side of film (A) is at the highest 3 mm, the bondingspots (2) are arranged on the crests of the flutes of (A) on the sidefacing (B), the distance (104) from middle to middle of adjacent spots(2) measured along the flutes, is at the highest 3 mm, and eachencapsulated pocket comprises at least 2 flutes, where the film (B) alsohas a fluted shape the pitch of said flutes (105) measured from middleto middle of adjacent flutes on the same side of film (B) is at thehighest 3 mm, and the bonding spots (2) are arranged on the crests ofthe flutes on the side of (B) facing (A) and wherein the film (A) issupplied with cup shaped or trough shaped bosses, and the spot-bondingis localized to crown portions or base portions of the bosses. However,there is the alternative possibility that one film (A) is supplied withcup shaped or trough shaped bosses, whereby the spot-bonding islocalised to crown portions or base portions of all or some of thebosses, as further explained below. A third film (C), supplied withsimilar bosses, may be included in such laminate. These possibilities acrosslaminate wherein the film (A) is supplied with cup shaped or troughshaped bosses, and the spot-bonding is localized to crown portions orbase portions of the bosses, wherein the film (B) is an unembossed film,in form of a coat produced by extrusion coating so as to establish theorientation of (B) as a longitudinal melt orientation, and to establishthe spot-bonding simultaneous with the coating when the molten (B)touches the crown portions or based portions of bosses on (A), thelamination pressure being adjusted such that more than 50% of the filmarea is left unbonded, whereas the dominating direction of orientationof (A) forms an angle to the longitudinal direction, further comprises athird film (C) on the side of (A) which is opposite to (B) which film(C) is uniaxially oriented or is biaxially oriented with one directiondominating, and which also is supplied with cup shaped or trough shapedbosses, and the film (B) is an unembossed film in form of a tie layerproduced by extrusion lamination so as to establish the orientation of(B) as a longitudinal melt orientation, and to establish thespot-bonding when the molten (B) touches the crown portions or baseportions of bosses on (A) and the crown portions or base portions ofbosses on (C), the laminate pressure being adjusted such that more than50% of the area of each of the films (A) and (C) is left unbonded,whereas the dominating directions of (A) and (C) from an angle to thelongitudinal direction, wherein the dominating direction of (C) crossesthe dominating direction of (A) and a crosslaminate comprising at leasttwo bonded-together films (A) and (B), each comprising an orientable,crystalline thermoplastic polymer material and each being uniaxiallyoriented or being biaxially oriented with one direction dominating, saiddirections in (A) and (B) crossing each other, the bonding comprising aspot bonding, where a) the gauge of each of the films (A) and (B) is atthe highest 30 g m⁻² in the form it has in the crosslaminate, b) film(A) is supplied with cup shaped or trough shaped bosses, thespot-bonding being localized to crown portions or to base portions ofsuch bosses on one side of film (A), c) film (B) is an unembossed film,d) the bonding between the film (A) and the film (B) is a spot bondingestablished on crown portions or base portions of bosses on (A) while atleast 25% and preferably at least 50% is kept free of bonding, and e)the dominating direction of orientation in (A) forms an angle higherthan zero and preferably higher than 10° to the longitudinal direction.By “cup shaped or trough shaped bosses” is meant spots of the film inwhich both surfaces protrude to the same side. The spots can beelongated in on direction. Examples of such embossment are given orreferred to in WO9112125, U.S. Pat. No. 5,205,650 FIGS. 1, 2 a, 2 b and3, and the microphotos shown in WO2009090208.

The word “bosses” is also occasionally used to indicate spot or linewhich is essentially thicker than the adjacent film material, andthereby protruding to both sides of the film but this is not the meaningin the present specification.

The crosslaminate consisting of an embossed film and an unembossed filmcan be characterised as a “cellular crosslaminate”. In the descriptionabove it is mentioned than film (B) can be bonded either to crownportions or to base portions of bosses on (A). The above mentionedFigures in U.S. Pat. No. 5,205,650 show a clear distinction between thebases of bosses on one side and crowns on the other side, and it is easyto image film (B) laminated to one or the other side of this embossedfilm. (These Figures show an embossment confined to a limited part ofthe film, but the description of the patent teaches that the embossmentmay comprise the entire film). Contrary to these Figures, themicrophotos in WO2009090208 show a waved type of embossment with crownson both sides of the film and no base portions of the bosses, and it iseasy to imagine film (B) laminated to crown portions on one or the otherside of this embossed film.

The film (B) which is laminated to the embossed film (A) is a flat filmprior to the lamination, but due to the laminate forces and subsequenttendency to shrinkage, film (B) may in the final laminate have lost itsflatness.

It is noted that the low weight crosslaminate structure, comprising thefilm (A) with cup shaped or trough shaped bosses, and the unembossedfilm (B), which has been formed by extrusion coating, and thereby hasjust “kissed” film (A) and formed spot bonds, in itself is consideredinventive independent of the formation of pockets to encapsulate thegas. This second aspect of the invention is a crosslaminate comprisingat least two bonded-together films (A) and (B), each comprising anorientable, crystalline thermoplastic polymer material and each beinguniaxially oriented or being biaxially oriented with one directiondominating, said directions in (A) and (B) crossing each other, thebonding comprising a spot bonding, where a) the gauge of each of thefilms (A) and (B) is at the highest 30 g m⁻² in the form it has in thecrosslaminate, b) film (A) is supplied with cup shaped or trough shapedbosses, the spot-bonding being localized to crown portions or to baseportions of such bosses on one side of film (A), c) film (B) is anunembossed film, d) the bonding between the film (A) and the film (B) isa spot bonding established on crown portions or base portions of bosseson (A) while at least 25% and preferably at least 50% is kept free ofbonding, and e) the dominating direction of orientation in (A) forms anangle higher than zero and preferably higher than 10° to thelongitudinal direction. The purpose of this second aspect of theinvention is to provide a low weight crosslaminate with improvedstiffness, feel of substance and a textile like handle. A method ofcrosslaminating films comprising the steps: 1) arranging two films (A)and (B), each comprises an orientable, crystalline thermoplastic polymermaterial and being uniaxially oriented or being biaxially oriented withone direction dominating, in face-to-face relationship with the theorientation directions in (A) and (B) crossing one another; 2) bondingthe films to one another by a spot-bonding process to form acrosslaminate, where: a) a gauge of each of the films (A) and (B) is atthe highest 30 g m⁻², measured as in the laminate; b) film (A) as usedin step 1) has cup shaped or trough shaped bosses; c) the bonding instep 2) is localized to cover crown portions or base portions of thebosses on the side of the film (A) facing film (b); d) film (B) isformed as an unembossed film by extrusion carried out in a manner toestablish its orientation as a longitudinal melt orientation and as toestablish the spot-bonding in step 2) as the molten material of (B)touches the crown or base portions of bosses on film (A) while keepingat least 25%, preferably at least 50%, of the facing area of the filmswithout any bonding, and wherein the said orientation of film (A) is atan angle to the longitudinal direction.

To increase the tear propagation resistance and the peel strength of thelaminate, the films may further be bonded together by curved or rectilinear bonds, which for these purposes need not form gastight pockets.

Most processes to produce cup or trough shaped bosses will make the filmin these bosses thinner than the surrounding film. However, in thestructure described below, most of the film portions in the bosses arethicker than the adjacent film portions, and this is an advantage forthe stability of the structure.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated in the accompanying sketches.

FIG. 1 shows a crosslaminate of two oriented films (A) and (B), whichboth are fluted. In each film the main direction of orientationcoincides with the direction in which its flutes extend.

FIG. 2 shows a crosslaminate of an embossed film (A), which is orientedunder acute angles to the machine direction, and a generally flat film(B) formed by extrusion coating, by which it has received meltorientation in the machine direction. During the coating the two filmshave “kissed” each other to form spot-bonding, such that more than 50%of the film area is left unbonded.

FIG. 3 shows this special carrying out of extrusion coating, referred toas the second aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION

As already stated, a main objective of both aspects of the invention isto reduce the square meter weight of crosslaminates while stillobtaining good stiffness with respect to bonding and especially a feelof substance. Accordingly, a crosslaminate comprising at least twobonded-together films (A) and (B), each comprising an orientable,crystalline thermoplastic polymer material and each being uniaxiallyoriented or being biaxially oriented with one direction dominating, thedirections in (A) and (B) crossing each other, the bonding being anintermittent bonding which leaves more than 50% of the film areaunbonded and which forms pockets to encapsulate gas, whereby the gaswithin each pocket has a volume which referring to the relaxed state ofthe laminate and 1 atmosphere ambient pressure is at least double thevolume of the polymer material, where a) the gauge of each of the films(A) and (B) is at the highest 30 g m⁻² in the form it has in thecrosslaminate, b) the bonding consists in a combination of a pattern ofrectilinear or curved bonding lines (4), which are combined to form thegas encapsulating pockets, and within each pocket at least 5 spot bonds(3), and c) the longest extension of each pocket in any direction is atthe highest 50 mm. set the limit of 30 g m⁻² for the gauge of each ofthe films (A) and (B) in the form which the film has in thecrosslaminate and a crosslaminate comprising at least twobonded-together films (A) and (B), each comprising an orientable,crystalline thermoplastic polymer material and each being uniaxiallyoriented or being biaxially oriented with one direction dominating, saiddirections in (A) and (B) crossing each other, the bonding comprising aspot bonding, where a) the gauge of each of the films (A) and (B) is atthe highest 30 g m⁻² in the form it has in the crosslaminate, b) film(A) is supplied with cup shaped or trough shaped bosses, thespot-bonding being localized to crown portions or to base portions ofsuch bosses on one side of film (A), c) film (B) is an unembossed film,d) the bonding between the film (A) and the film (B) is a spot bondingestablished on crown portions or base portions of bosses on (A) while atleast 25% and preferably at least 50% is kept free of bonding, and e)the dominating direction of orientation in (A) forms an angle higherthan zero and preferably higher than 10° to the longitudinal direction.However, this gauge can with advantage be at the highest 20 g m⁻² oreven no more than 15 g m⁻².

Process steps for manufacture of the crosslaminate which exhibitedfluted shape, as these crosslaminates wherein the film (A) has a flutedshape, the pitch of the flutes (103) measured from middle to middle ofadjacent flutes on the same side of film (A) is at the highest 3 mm, thebonding spots (2) are arranged on the crests of the flutes of (A) on theside facing (B), the distance (104) from middle to middle of adjacentspots (2) measured along the flutes, is at the highest 3 mm, and eachencapsulated pocket comprises at least 2 flutes and wherein the film (B)also has a fluted shape the pitch of said flutes (105) measured frommiddle to middle of adjacent flutes on the same side of film (B) is atthe highest 3 mm, and the bonding spots (2) are arranged on the crestsof the flutes on the side of (B) facing (A), appear from the abovementioned publications WO02/102592 Rasmussen and WO04/54793 Rasmussen,but in the first aspect of the present invention, to these well knownsteps there must be added the step of further sealing the films togetherin a pattern of rectilinear or curved lines (1), which are combined toform the gas encapsulating pockets, each surrounding at least 5 of thespot bonds, which were formed by the known steps. The longest extensionof each pocket in any direction is at the highest 50 mm, preferably atthe highest 30 mm and preferably at least 6 mm.

An embossed film, which for the reason stated above is particularlysuitable for manufacture of the product described herein, is disclosedin WO2009090208. This was not published when the priority forming patentapplication for the present application was filed. Such film is formedof thermoplastic polymer material and comprises an array of parallelband-shaped, linearly extending regions (a) and distinct therefromlinearly extending webs (b) which integrally connect said regions. Eachweb (b) is at each location of its linear extension thinner than theadjacent portions of regions (a).

In this film both (a) and (b) are oriented having at each location adominating direction of orientation. The film is characterized in thatthe dominating direction of orientation in the regions (a) forms angles(v) higher than zero but no higher than 80° with the direction in which(a) extends, and the webs (b) comprise arrays of linear furrows (c)which are necking-down zones, said furrows forming angles (u) higherthan (v) to the directions in which (a) extends. The film for use in thepresent invention is further characterised in that the regions arewaved, each wave extending over the width of such region and the websbeing shorter than the adjacent parts of the regions (a) so as to force(a) to wave. It is this waving which forms the cup or trough shapedbosses.

The method of producing such film starts with a film having apredominant direction of orientation. The film is stretched by means ofa pair of mutually intermeshing first grooved rollers in a directionwhich is different, but at the highest 80° different, from thepredominant original direction of orientation in the film. The method ischaracterized in that at least one of the grooved rollers in the pairhas crests with edges which are sufficiently sharp to form a distinctdivision between parallel, linearly extending webs (b) of film material,which have been coldstretched between the crests of the two firstgrooved rollers and intervening linearly extending band-shapes regions(a), which have laid on the sharp edged crests and have not beenstretched or have been stretched to a smaller extend between the saidgrooved rollers. The contraction which produces the waving of (a) andthereby the bosses, arises inherently if not counteracted.

In the first aspect of the invention, the pattern bonding lines toencase air consists in its simplest form, two arrays each of parallelstraight lines, which arrays crisscross each other. This can be done bymeans of two pairs of sealing rollers, one pair working in succession tothe other, and each pair consisting of a hot steel roller workingagainst a hot, silicone rubber coated roller. One of the steel rollersmay be supplied with a pattern of circular crests, e.g. 0.5 mm wide, andthe other with axial cogs, e.g. also 0.5 mm wide. Alternatively they mayboth be supplied with a pattern of helical crests one right turned andthe other left turned.

In a more advanced form this pattern is a honeycomb pattern. Thisprovides better stiffness, but requires more expensive sealing rollers.One roller can be a hot patterned steel roller, working against a hotsilicone rubber coated roller.

These two patterns are only examples of the shapes of the pockets. It isnoted that the pattern of bonding lines (4) which form the pocket forencapsulation of air, additionally has the function that it increasesthe tear propagation resistance and the peel strength of the laminate.

During the sealing process to form pockets and encapsulate gas (normallyair) the ambient pressure may be kept somewhat higher than the normalatmospheric pressure to achieve a suitable internal tension in the finallaminate.

Each bonding between the films (A), (B) and optionally (C) is preferablyestablished through one or more coextruded lamination layers.

Most conveniently, more than 50% of each film (A) and (B) consists ofHDPE, LLDPE, crystalline PP or blends or copolymers based onpolyethylene or polypropylene.

While the first and second aspect of the present invention primarilyhave been conceived with a view to water impermeable packaging film,they can also be applied to breathable film, e.g. for sanitary purposes.To this end there may be perforations collected in distinct areas, whichareas are interspersed with the air encapsulating pockets.

In conventional extrusion lamination of two solid films or in extrusioncoating, which consists in laminating a directly extruded film to apreformed solid film, the lamination takes place between rollers, andthere is applied a relatively high lamination pressure, since otherwiseair may be entrapped. However, in the present invention an aim is toentrap a big volume of air, forming a cellular kind of product. Toachieve this, a method of laminating a solid film with a molten directlyextruded flat film while introducing spaces of gas between the twofilms, where the lamination pressure is established on one side of thefilm assembly in the form of a pressurized air film, and on the otherside either by a roller surface or by a pressurized air film and anapparatus for extrusion coating a solid film or extrusion laminating twosolid films, comprising a flat die for mono- or co-extrusion of a film,and means to bring the solid and the extruded film in face-to-facerelationship as an assembly and apply a laminating pressure while atleast each surface of the extruded film is in molten or semi moltenstate, where the means to apply a lamination pressure comprise on oneside of the assembly first means to form a first pressurized air film,and on the other side either a roller surface or a second means to forma second pressurized air film, further comprising means to adjust theair pressure exercised on the assembly with subclaims are highlypreferable. The formulation of a pressurized air film, normally underuse of a microporous wall in a die through which an air flow is pressed,is commonly used as “air lubrication” for many different purposes. Inthe present invention it is also used as means to set up an easilyadjustable and low lamination pressure which at least on one side iscontactless, and which enhances the entrapment of air. In thisconnection it is advantageous but not in all cases necessary that thesolid film has been embossed before the lamination.

A pressurized air film is normally, as explained above, produced bypressing the air through a die wall consisting of microporous material.This is normally formed by sintering. Alternatively the die wall may besupplied with a great multitude of fine holes, e.g. formed by lasertreatment. In the present invention the pressurized air film may also beformed by a single slot which traverses the entire width of the filmassembly e.g. of 0.1-0.2 mm gap, formed by laser treatement or sparkerosion.

The laminating pressure can be adjusted by adjustment of the spacing ofthe air film or air films and/or by adjusting the air flows.

In FIG. 1 lines (1) show the middle of the longitudinally extendingoutside crests of the flutes on film (A).

Similarly, lines (2) show the middle of the transversely extendingoutside crests of the flutes on film (B). The dots (3) show thespot-bonding, which has been established between portions of the twoarrays of inside crests. This structure can be made by the proceduredescribed in the example of WO04/54796 Rasmussen, except for the gaugeof the films (A) and (B), which must be lower. A perspective view ofthis structure is shown in FIG. 1 in the same patent specification.

The new feature is the two arrays of sealing lines (4), which cross eachother. Preferably this sealing is made absolutely tight to encase theair.

As in the above mentioned example, the bonding between the films isestablished through coextruded lamination layers.

In addition to the primary function to encase air, such pattern ofsealing lines also serves to improve the tear propagation resistance.For that purpose the sealing needs not be tight, and a “semi-encasing”pattern of rectilinear or curved lines will be satisfactory.

FIG. 1 shows the wavelength in both films (A) and (B) being 1 mm, theencasement being square formed with edge 10 mm, and the width of thelinear seals being 0.5 mm. These measures are generally convenient, butbig variations are possible.

In FIG. 2 the dots (3) here shown elongated in the machine direction,again illustrate the spot-bonding between the films (A) and (B). Thebonding is established between protruding cup shaped or trough shapedbosses by an extrusion coating process, which in principle is shown inFIG. 3. The embossed film (A), which is molecularly oriented on bias,preferably has a structure disclosed in WO2009090208, briefly explainedabove in the general description, and may conveniently consist of HDPE.The coating may e.g. consist of LLDPE, LDPE, or a lower melting ethylenecopolymer.

As a matter of simplification of the sketch, FIG. 2 shows thespot-bonding in a very regular pattern, but in actual fact it will bemore randomized.

In FIG. 3 the embossed film (A) with orientation on bias is fed into thecoating device as shown by the arrow (5). It may be taken from a reel ormay come directly from the embossment station. The molten film (B) comesfrom a flat extrusion die (6) and becomes melt oriented in the machinedirection by the draw-down, e.g. from exit slot gap 0.25-0.5 mm to afinal thickness between 5-20 micrometer.

The coating takes place between the two very schematically shown airfilm forming dies (7) and (8). The edge (9) of die (7), over which film(A) bends, is rounded, e.g. with radius about 1 cm. The surfaces of thetwo dies, which face the two films, are produced from microporousmaterial to form pressurized air films, and so is the rounded edge (9).The pressurized air film formed by die (7) and blowing on film (A) hasambient temperature, while the pressurized air film formed by die (8)and blowing towards film (B) has a temperature essentially lower thanthe exit temperature of the extrusion die (7) but high enough to causebonding.

The coated film is a crosslaminate of the embossed film (A), which isoriented on bias, and the coat, which is melt oriented in the machinedirection. It is hauled off by the cooling roller (11) and the rubberroller (12). The two rollers are driven by the same circumferentialvelocity.

They are very close to each other, but to avoid ruining of the embossedstructure they don't press against each other.

The cross laminate (10) proceeds to winding (not shown). All the waythrough the shown process the tension is kept sufficiently low to avoidruining of the embossment. The devices for this are not shown.

A suitable bonding, leaving more than 25% of the film area unbonded, isproduced by adjustments of 1) the temperature at which film (B) leavesthe extrusion die, 2) the positions of dies (7) and (8), 3) thetemperature of the air film produced by die (8), and 4) the airvelocities of the two air streams.

The adjustment is such that the two films only “kiss” each other.

Between roller (12) and the spooling up there may be sealing rollers toform the lines (4) shown in FIG. 2. These may consist of a hot patternedsteel roller working against a hot silicone rubber coated roller.

EXAMPLE 1

In this and the following two examples the process and apparatus arebasically as described in connection with FIG. 3. The flat extrusion die(6) is constructed for coextrusion of two components. The gap of theexit orifice is 0.5 mm. In the present example 8-0% of the extruded filmconsists of HMWHDPE of d=0.95 density 0.95 g/mL and 20% of an ethylenecopolymer (“Attane”) melting at about 90° C. and of m.f.i.=1.0. Thelower melting layer is supplied on the side which will face the solidfilm. The extrusion temperature is 270° C. The extrusion throughput andthe velocity of rollers (11) and (12) are adjusted to produce a filmthickness calculated of to become 10 micrometers. By the longitudinaldraw down in the ratio 50 to 1 the extruded film gets a strong meltorientation.

The solid film (A) is the single film produced according to example 3 inWO2009/090208. It is deeply embossed with crests of bosses protrudingfrom each side. It is biaxially oriented, differently within differentnarrow regions, but with a direction near 45° dominating. While itadvances towards the die (7) which supplies a pressurized air film ofambient temperature, all tendencies to wrinkling are removed by means ofa driven “banana roller”. The tension in film (A) when it meets the airdie (7) is adjusted to be near zero so as to maintain maximum degree ofembossment. It is turned so that its low melting side will face theextruded film (B).

Throughout the air die (8), which is heat insulated, hot air is blown.The temperature of the air as it exits this die is adjusted to 100° C.The space between dies (7) and (8) is about 5 mm, and the length of thezone in which the two films are under air pressure is above 20 mm. Thedistance from the exit orifice of the extrusion die (6) to the twoair-dies (7) and (8) is also about 20 mm.

The air for the two dies (7) and (8) are taken from the same airreservoir, the pressure of which is adjustable, and the resistance toair flow through the microporous walls in the two dies is practicallyequal, thus the air filing of both sides have practically the samepressure. The air for die (8) is heated before it meets the die (8).

Between the dies (7) and (8) and the first haul off roller (17) air ofambient temperature is blown onto the laminated film assembly (10). Thisis not shown in the drawing.

By trial and error the pressure in the air reservoir is adjusted to avalue which produces the desired degree of lamination, i.e. the desiredpercentage of bonded areas. This may conveniently be above 25-30%. It isdetermined by microscopy of samples.

EXAMPLE 2

This deviates from example 1 in that the extruded film is a one layerfilm consisting of the copolymer (Attane) which formed the laminationlayer on the extruded film of example 1. In all other respects example 1is followed.

In this procedure the extrusion die could have been a monoextrusion die,and this would be a simplification. When using such monoextrusion it isexpected that plain LLDPE or HDPE would be applicable in spite of thehigher melting points, but this would make the adjustment of coolingconditions more complicated.

EXAMPLE 3

In this example the invention is used for extrusion lamination of twosolid films with mutually crossing directions of orientation. These twofilms are the same as the solid film (B) used in examples 1 and 2. As inexample 2 the extruded film (B) is the copolymer of (Attane) havingmelting point around 90° C., and its thickness in the laminate is about10 micrometers.

The extruded film (B) is applied between the two solid films, thus theline shown in FIG. 3 is supplemented by apparatus for feeding theadditional solid film over the air die (8), and the latter has a roundededge like edge (9) on die (7).

In this case air of ambient temperature is used for both pressurized airfilms formed by dies (7) and (8), and there is applied an adjusted flowof cooling air to the extruded film between the exit orifice of theextrusion die (6) and the two air dies (7) and (8).

We claim:
 1. A method of manufacturing a crosslaminate comprising atleast two bonded-together films (A) and (B), each comprising anorientable, crystalline thermoplastic polymer material in which each issupplied with uniaxial orientation or being biaxially oriented with onedirection dominating, and the directions in films (A) and (B) is broughtto cross each other, bonding being carried out as an intermittentbonding which leaves more than 50% of the film area unbonded and whichforms pockets to encapsulate gas, whereby the gas within each pocket hasa volume which referring to the relaxed state of the laminate and 1atmosphere ambient pressure at least is double the volume of the polymermaterial, where a) the gauges of starting materials and conditions oforientation are such that the gauge of each of the films (A) and (B) isat the highest 30 g m⁻² in the form it has in the crosslaminate, b) thebonding is carried out as a combination of a patterns of rectilinear orcurved bonding lines (4), which are combined to form the gasencapsulating pockets, and within each pocket at least 5 spot bonds (3)and such that c) the longest extension of each pocket in any directionis at the highest 50 mm.
 2. A method of crosslaminating films comprisingthe steps: 1) arranging two films (A) and (B), each comprises anorientable, crystalline thermoplastic polymer material and beinguniaxially oriented or being biaxially oriented with one directiondominating, in face-to-face relationship with the orientation directionsin (A) and (B) crossing one another; 2) bonding the films to one anotherby a spot-bonding process to form a crosslaminate, where: a) a gauge ofeach of the films (A) and (B) is at the highest 30 g/m², measured as inthe laminate; b) film (A) as used in step 1) has cup shaped or troughshaped bosses; c) the bonding in step 2) is localised localized to covercrown portions or base portions of the bosses on the side of the film(A) facing film (b); d) film (B) is formed as an unembossed film byextrusion carried out in a manner to establish its orientation as alongitudinal melt orientation and as to establish the spot-bonding instep 2) as the molten material of (B) touches the crown or base portionsof bosses on film (A) while keeping at least 25%, of the facing area ofthe films without any bonding, and wherein the said orientation of film(A) is at an angle to the longitudinal direction.
 3. The methodaccording to claim 2, further comprising step 3) after or simultaneouslywith step 2) of bonding the two films together by curved or straightlinear bonds.
 4. The method according to claim 3, wherein the bonding instep 2) involves blowing pressurized air against one or both outwardfacing sides of the pair of films (A) and (B) after the longitudinalorientation of film (B).
 5. The method according to claim 4, wherein thepressurized air directed on the (B) film side of the film pair is heatedto a temperature lower than the extrusion temperature but generallyequal to or higher than the temperature required for the spot-bonding totake place.
 6. A method of laminating a solid film with a moltendirectly extruded flat film while introducing spaces of gas between thetwo films, where the lamination pressure is established on one side ofthe film assembly in the form of a pressurized air film, and on theother side either by a roller surface or by a pressurized air film.